title: Elucidation of the human serum albumin (HSA) binding site for the Cu-PTSM and Cu-ATSM radiopharmaceuticals.
abstract: The Cu-PTSM (pyruvaldehyde bis(N(4)-methylthiosemicarbazonato)copper(II)) and Cu-ATSM (diacetyl bis(N(4)-methylthiosemicarbazonato)copper(II)) radiopharmaceuticals exhibit strong, species-dependent binding to human serum albumin (HSA), while Cu-ETS (ethylglyoxal bis(thiosemicarbazonato)copper(II)) appears to only exhibit nonspecific binding to human and animal serum albumins. This study examines the structural basis for HSA binding of Cu-PTSM and Cu-ATSM via competition with drugs having known albumin binding sites. Warfarin, furosemide, ibuprofen, phenylbutazone, benzylpenicillin, and cephmandole were added to HSA solutions at drug:HSA mole ratios from 0 to 8:1, followed by quantification of radiopharmaceutical binding to HSA by ultrafiltration. Warfarin, a site IIA drug, progressively displaced both [(64)Cu]Cu-PTSM and [(64)Cu]Cu-ATSM from HSA. At 8:1 warfarin:HSA mole ratios, free [(64)Cu]Cu-PTSM and [(64)Cu]Cu-ATSM levels increased 300-500%. This was in contrast to solutions containing ibuprofen, a site IIIA drug; no increase in free [(64)Cu]Cu-PTSM or [(64)Cu]Cu-ATSM was observed except at high ibuprofen:HSA ratios, where secondary ibuprofen binding to the IIA site may cause modest radiopharmaceutical displacement. By contrast, and consistent with earlier findings suggesting Cu-ETS exhibits only nonspecific associations, [(64)Cu]Cu-ETS binding to HSA was unaffected by the addition of drugs that bind in either site. We conclude that the species-dependence of Cu-PTSM and Cu-ATSM albumin binding arises from interaction(s) with the IIA site of HSA.
authors.affiliation: Division of Nuclear Pharmacy, Department of Industrial and Physical Pharmacy, Purdue University, 575 Stadium Mall Drive, West Lafayette, Indiana, USA.
authors.forename: Nathan E
authors.initials: NE
authors.lastname: Basken
authors.forename: Carla J
authors.initials: CJ
authors.lastname: Mathias
authors.forename: Mark A
authors.initials: MA
authors.lastname: Green
mesh_terms: D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D056831:Coordination Complexes; D004285:Dogs; D005227:Fatty Acids / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D009942:Organometallic Compounds / Q000737:chemistry / Q000378:metabolism*; D004364:Pharmaceutical Preparations / Q000378:metabolism*; D011485:Protein Binding; D051381:Rats; D012709:Serum Albumin / Q000737:chemistry* / Q000378:metabolism*; D013882:Thiosemicarbazones / Q000737:chemistry / Q000378:metabolism*
chemical_list: D056831:Coordination Complexes; D005227:Fatty Acids; D009942:Organometallic Compounds; D004364:Pharmaceutical Preparations; D012709:Serum Albumin; D013882:Thiosemicarbazones; C089548:copper (II) diacetyl-di(N(4)-methylthiosemicarbazone); C052629:copper pyruvaldehyde bis(N(4)-methylthiosemicarbazone) complex